U.S. Pat. No. 4,895,841 and U.S. Pat. No. 6,277,866 disclosed piperidine derivatives having excellent anti acetyl cholinesterase activity. These compounds are effective for treatment and prevention of diseases such as Alzheimer senile dementia, Huntington's chorea, Pick's disease and ataxia. Of these compounds, donepezil hydrochloride, 1-benzyl-4-[(5,6-dimethoxy-1-indanon-2-yl)methyl]piperidine hydrochloride is a well known acetyl cholinesterase inhibitor and is on the market as Aricept for the treatment of Alzheimer disease.
According to the process disclosed in U.S. Pat. No. 4,895,841, 5,6-dimethoxy-1-indanone was condensed with 1-benzyl-4-formylpiperidine in the presence of lithium diisopropylamide to give 5,6-dimethoxy-2-[[1-benzyl-4-piperidinyl]methylene]-1-indanone, which was then reduced with platinum oxide catalyst to give donepezil.
1-Benzyl-4-formylpiperidine is not available and difficult to synthesize commercially. Moreover the combined yield is very low.

U.S. Pat. No. 5,606,064 disclosed a process for the preparation of donepezil. 5,6-dimethoxy-1-indanone was condensed with pyridin-4-aldehyde to give 5,6-dimethoxy-2-(pyridin-4-yl)methyleneindan-1-one, reacted with benzyl bromide to give 1-benzyl-4-(5,6-dimethoxyindan-1-on-2-ylidene)methylpyridinium bromide and then, hydrogenated in the presence of platinum oxide catalyst to yield donepezil.
The yield of the hydrogenation of pyridinium salt is 81%.

According to WO 9722584, methyl 4-[2-(3,4-dimethoxybenzoyl)ally]piperidin-1-carboxylate is cyclized in the presence of sulfuric acid to give methyl 4-(5,6-dimethoxy-1-oxoindan-2-ylmethyl)piperidin-1-carboxylate, decarboxylated and then treated with benzyl bromide to give donepezil.
Preparation of methyl 4-[2-(3,4-dimethoxybenzoyl)allyl]piperidin-1-carboxylate intermediate itself involve many stages thereby resulting in very low overall yield.

According to U.S. Pat. No. 6,252,081, 5,6-dimethoxy-2-methoxycarbonyl-1-indanone is reacted with 4-pyridinylmethyl chloride to give 5,6-dimethoxy-2-(4-pyridyl)methoyl-2-methoxycarbonyl-1-indanone, decarboxylated to give 5,6-dimethoxy-2-(4-pyridyl)methyl-1-indanone then, reacted with benzyl bromide to give 1-benzyl-4-[(5,6-dimethoxy-1-indanon)-2-yl]methylpyridinium bromide followed by catalytic hydrogenation to yield donepezil.
The process involves introduction of methoxy carbonyl group and decarboxylation steps, thereby making the process very lengthy.

Indanone derivatives of the formula I are useful intermediates for the preparation of acetyl cholinesterase inhibitors of the formula III. The major problem with the preparation of the compounds of the formula I by the catalytic hydrogenation of the compound of the formula II is that high pressures are required and that under these conditions carbonyl group is also reduced to alcohol.
We have found that the compounds of the formula II can be selectively hydrogenated to yield the compounds of the formula I using hydrogenating catalyst under a suitable condition. The yields and purities are found to be very good.
The intermediates of the formula I can be converted to the compounds of formula III by the method described in example 180 of EP 296560 and WO 9722584.
The compounds of the formula II can be easily and cheaply obtained from the processes described in J. Heterocyclic Chem. 2(4), 366-370 (1965) and U.S. Pat. No. 5,606,064.
Thus, the present invention provides a simple, cost effective and industrial process for the preparation of the compounds of the formula III via the intermediates of the formula I and overcomes the problems of the prior art processes.